Several studies have reported the use of .sup.99m Tc-sestamibi (mibi=CNCH.sub.2 C(CH.sub.3).sub.2 (OCH.sub.3)) for imaging various tumors including breast, Clin. Nucl. Med. 17:171-176, thyroid, parathyroid, bone, lung and brain. .sup.99m Tc-sestamibi appears to have a high sensitivity (&gt;90%) and acceptable specificity (&gt;70%) for imaging breast tumors, J. Nucl. Med. 1993, 34:149P. .sup.99m Tc-sestamibi localizes within the mitochondria of tissues and the mechanism appears to be the attraction of the lipophilic cationic complex to the negative potential on the inner mitochondrial membrane. .sup.99m Tc-sestamibi is retained in human tumors and is currently in clinical trial as a diagnostic agent for imaging of breast tumors.
.sup.99m Tc-tertiary-butyl isonitrile complex (.sup.99m Tc-TBI) has previously been described in U.S. Pat. No. 4,452,774 (Jones et al) and U.S. Pat. No. 4,988,827 (Bergstein et al). In Example 5 of Bergstein et al, it was shown that .sup.99m Tc-TBI is an inferior myocardial imaging agent compared with the ether isonitriles described therein due to .sup.99m Tc-TBI's low heart/liver and heart/lung uptake ratios. Bergstein et al did not test for tumor imaging agents and did not suggest using .sup.99m Tc-TBI or .sup.186/188 Re-TBI as a breast tumor imaging agent.
Ramanathan et al, J. Nucl. Med. 1990, 31(7), 1163, indicate that .sup.99m Tc-TBI can be used to image a suppressed thyroid lobe in place of the thyrotropin stimulation test. However, there is no mention in this article of using .sup.99m Tc-TBI as a tumor imaging agent.
Even though .sup.99m Tc-sestamibi is an excellent tumor imaging agent, other agents providing enhanced sensitivity and specificity in tumor imaging could significantly impact on patient care. This would translate to detecting smaller (earlier) tumors and/or better resolution in difficult-to-image patients. The vast number of patients diagnosed with tumors provides the impetus for finding imaging agents which provide greater uptake and retention compared with those presently known.